1. Field of the Invention
The present invention relates to integrated circuit device packaging, and more specifically, to an interposer substrate capable of reducing cross-talk between signal lines which is suitable for interconnecting integrated circuit chips to a printed circuit board or other substrate.
2. Description of the Prior Art
An interposer is a structure used in the manufacture of single and multi-chip modules (SCMs or MCMs) to electrically connect one or more integrated circuit chips (ICs) to a printed circuit board or other substrate. The interposer provides power and ground connections between the board or substrate and the ICs. The interposer also provides signal paths between the IC chips and the board or substrate, and if desired, between different chips mounted on the interposer. An interposer thus provides a means of interconnecting signal, power, and ground lines between a substrate, an integrated circuit chip or chips, and ultimately a package containing the chip(s).
As the number of components in electronic devices increases and the size of the individual components decreases, there is an increase in the number and density of power, ground, and signal interconnections needed between individual ICs and the substrate to which the chips are connected. This means that the density of the interconnections which need to be included as part of an interposer also increases. However, problems arise in placing signal lines in close proximity to each other and to power supply lines when fabricating such an interposer. These problems include interference and cross-talk arising from coupling between the lines on a common layer or between signal lines on different signal layers, and capacitive coupling between the lines and the substrate which produces noise in the signals. In conjunction with the separation between the various lines, the dielectric constant of the substrate material thus plays an important role in reducing (or creating) these type of problems.
Another disadvantage of conventional approaches to packaging IC chips in MCMs arises from the method used to deliver power to the chips. This problem results because power lines are typically routed through the same substrate which is utilized to carry signals to and from the chip. The power feedthroughs will compete for space with the signal I/O lines. This will further increase the problems caused by densely packed signal traces. Another important disadvantage is that the thinness of the substrates used in traditional multichip modules results in the power feeds to the IC chips having a relatively high impedance. This results in undesired noise, power loss, and excess thermal energy production. These problems are relevant to the routing of both power and signal lines though an interposer substrate.
What is desired is an interposer for interconnecting a single integrated circuit chip to a substrate, or for interconnecting a plurality of chips to each other and to a substrate, which addresses the noted disadvantages of conventional structures.